Cordless telephones having a cordless handset and enabling a conversation with a person at a distance from a base unit connected to a telephone line are widely used. With this widespread use, situations where a plurality of radio communication systems exist in the same area have arisen. If the base unit always transmits a radio signal with the maximum power in such situations, although communication is made possible between the base unit and the handset at a distance from one another, there arises a problem in that the radio used for the communication causes significant interference to other radio communication systems.
Given this, cordless telephones variably controlling the transmission power of the base unit have been developed. For example, Japanese Patent Application Laid-Open No. 2001-332987 (hereinafter, referred to as “PTL 1”) discloses a technique that sets the optimum transmission power by making a control such that the transmission power value of a radio communication apparatus is made the maximum value at the start of communication and the transmission power value is reduced by a predetermined amount each time transmission succeeds and increased by a predetermined amount when transmission fails, for example.
Japanese Patent Application Laid-Open No. 2002-345026 (hereinafter, referred to as “PTL 2”) discloses a technique that controls the transmission power of the base unit (connection apparatus) in accordance with whether or not a handset is linked to a charging cradle. That is, PTL 2 discloses the technique whereby communication is done with a low transmission power when the handset is linked to the charging cradle and communication is done with a high transmission power when the handset is removed from the charging cradle. By doing this, the technique of PTL 2 enables maintenance of communication between a handset and a connection apparatus even if an interfering signal is received in the process of the handset moving away from the connection apparatus.